In an electrified vehicle, a contactor connects the battery pack to high-voltage electrical loads such as a traction motor. When the electrical contact surface of a contactor is clean and smooth, the contactor consumes nearly no power. However, the contact surface can be damaged or rendered unclean due to vehicle vibration, hazard gases, electric shock duration and other influences. The damaged or unclean surface may lead to increasing contact surface resistance.
The increase in surface resistance of a contactor may cause the contactor to consume a substantial portion of power, reducing the usable power which is available from the battery pack to drive the traction motor and/or charge the battery pack. The resistance, in turn, increases heat dissipation which may heat the contactor and further damage the contractor and battery pack. Because of the large battery current used in an electrified vehicle, the electrical power which is consumed by the contactor may be considerable even though the contact surface resistance may be very small. For example, if the contact surface resistance is as small as 0.1 ohm, the battery current may be as large as 200 Amp and the contactor may consume 4 KW electrical power.
The increasing surface resistance on the contactor may result in a failure mode in the electrified vehicle. Therefore, it may be desirable to define a diagnostic strategy to detect a failure mode which results from a compromised contact surface on a contactor in a battery pack.
Accordingly, a method for diagnosing a resistance failure mode of contactors on a battery pack may be desirable for some applications.